Evolutionarily recent transfer of a group I mitochondrial intron to telomere regions in Saccharomyces cerevisiae

The junctions between X and Y' subtelomeric repeats in Saccharomyces cerevisiae usually contain a stretch of telomere sequences, (G1-3T)n. Two of three cloned X-Y' junctions from strain YP1 have a replacement of about 200 bp of X, the internal telomere sequence, and 49 bp of Y' by a 292 bp sequence. The first 227 bp of this insertion sequence are 100% identical to the fourth intron of cytochrome b. The rest of the insertion has homology to an unknown dispersed nuclear sequence. Recombination among subtelomeric regions can explain the nuclear distribution of this sequence and why telomeres can trap and maintain sequences that would otherwise be lost.